In order to investigate the impact of zinc on immune response to OPV, the investigators would determine the status of zinc (serum levels) in infants in all the groups. These would be determined from blood samples collected at birth, at 6 weeks and at 18 weeks of age and analyzed using atomic absorption spectrophotometry using established micromethods. Other micronutrient indicators influencing systemic and mucosal immunity (hemoglobin, ferritin and vitamin A) would also be analyzed from the collected blood specimens of the recruited subjects.